Typically, to deposit a porous carbon on a base metal formed of a metallic material, a porous metal coating layer with a high adhesion needs to be formed on a surface of the base metal on which a thin film is deposited so as to allow metal and carbon to be combined with each other easily.
To do this, as a conventional coating layer forming method, a vacuum deposition method of performing deposition under vacuum conditions and a thermal spray method of performing deposition by heating are widely used.
Regarding the vacuum deposition method, a vapor or ion of metal or non-metal is heated under vacuum conditions and then attached to a base metal (an object to be coated), and regarding the thermal spray method, momentary high pressure heat and a source are simultaneously molten permeation coated on an object to be coated by spraying. Various coating methods including ceramic, metalizing, plasma coating, etc. are used according to a material to be applied.
However, the conventional vacuum deposition method necessarily requires an expensive vacuum chamber, which leads to high manufacturing costs. Also, the vacuum deposition method is not appropriate for forming a thick coating layer. Due to such limitations, the use of the vacuum deposition method is very restricted.
Also, the conventional thermal spray method uses high-temperature heat and thus, it is highly likely that a base metal, to which the heat is transferred, is deformed (distorted, etc.) In particular, if the thickness of the base metal is small, the deformation may easily occur, which makes the formation of a coating layer (also referred to as a buffer layer) difficult.
Accordingly, to resolve the problems described above, the present invention provides an inexpensive method of forming a coating layer with a sufficient adhesion with respect to a base metal at low temperature for a short period of time while deformation of the base metal is prevented when the coating layer is formed.